On Fri, 2007-10-19 at 12:20 +0800, Herbert Xu wrote:
>
> That's why I think this patch is in fact the only one that
> solves all the races in this thread. The case that it solves
> which the lock/unlock patch does not is the one where action
> flows downwards past the clearing of IRQ_INPROGRESS. I missed
> this case earlier.
>
> In fact this bug exists elsewhere too. For example, the network
> stack does this in net/sched/sch_generic.c:
>
> /* Wait for outstanding qdisc_run calls. */
> while (test_bit(__LINK_STATE_QDISC_RUNNING, &dev->state))
> yield();
>
> This has the same problem as the current synchronize_irq code.
The network stack always made be nervous with it's bitops use as locks.
Any loop of test_bit() alone as a synchronisation method, without locks
or barriers is, imho, inherently buggy.
Ben.
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